1
|
Scott L, Elídóttir K, Jeevaratnam K, Jurewicz I, Lewis R. Electrical stimulation through conductive scaffolds for cardiomyocyte tissue engineering: Systematic review and narrative synthesis. Ann N Y Acad Sci 2022; 1515:105-119. [PMID: 35676231 PMCID: PMC9796457 DOI: 10.1111/nyas.14812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Electrical conductivity is of great significance to cardiac tissue engineering and permits the use of electrical stimulation in mimicking cardiac pacing. The development of biomaterials for tissue engineering can incorporate physical properties that are uncommon to standard cell culture and can facilitate improved cardiomyocyte function. In this review, the PICOT question asks, "How has the application of external electrical stimulation in conductive scaffolds for tissue engineering affected cardiomyocyte behavior in in vitro cell culture?" The Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, with predetermined inclusion and quality appraisal criteria, were used to assess publications from PubMed, Web of Science, and Scopus. Results revealed carbon nanotubes to be the most common conductive agent in biomaterials and rodent-sourced cell types as the most common cardiomyocytes used. To assess cardiomyocytes, immunofluorescence was used most often, utilizing proteins, such as connexin 43, cardiac α-actinin, and cardiac troponins. It was determined that the modal average stimulation protocol comprised 1-3 V square biphasic 50-ms pulses at 1 Hz, applied toward the end of cell culture. The addition of electrical stimulation to in vitro culture has exemplified it as a powerful tool for cardiac tissue engineering and brings researchers closer to creating optimal artificial cardiac tissue constructs.
Collapse
Affiliation(s)
- Louie Scott
- School of Veterinary MedicineUniversity of SurreyGuildfordUK
| | | | | | | | - Rebecca Lewis
- School of Veterinary MedicineUniversity of SurreyGuildfordUK
| |
Collapse
|
2
|
Karvas RM, McInturf S, Zhou J, Ezashi T, Schust DJ, Roberts RM, Schulz LC. Use of a human embryonic stem cell model to discover GABRP, WFDC2, VTCN1 and ACTC1 as markers of early first trimester human trophoblast. Mol Hum Reprod 2021; 26:425-440. [PMID: 32359161 DOI: 10.1093/molehr/gaaa029] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Revised: 04/09/2020] [Accepted: 04/23/2020] [Indexed: 12/25/2022] Open
Abstract
Human placental development during early pregnancy is poorly understood. Many conceptuses are lost at this stage. It is thought that preeclampsia, intrauterine growth restriction and other placental syndromes that manifest later in pregnancy may originate early in placentation. Thus, there is a need for models of early human placental development. Treating human embryonic stem cells (hESCs) with BMP4 (bone morphogenic protein 4) plus A83-01 (ACTIVIN/NODAL signaling inhibitor) and PD173074 (fibroblast growth factor 2 or FGF2 signaling inhibitor) (BAP conditions) induces differentiation to the trophoblast lineage (hESCBAP), but it is not clear which stage of trophoblast differentiation these cells resemble. Here, comparison of the hESCBAP transcriptome to those of trophoblasts from human blastocysts, trophoblast stem cells and placentas collected in the first-third trimester of pregnancy by principal component analysis suggests that hESC after 8 days BAP treatment most resemble first trimester syncytiotrophoblasts. To further test this hypothesis, transcripts were identified that are expressed in hESCBAP but not in cultures of trophoblasts isolated from term placentas. Proteins encoded by four genes, GABRP (gamma-aminobutyric acid type A receptor subunit Pi), WFDC2 (WAP four-disulfide core domain 2), VTCN1 (V-set domain containing T-cell activation inhibitor 1) and ACTC1 (actin alpha cardiac muscle 1), immunolocalized to placentas at 4-9 weeks gestation, and their expression declined with gestational age (R2 = 0.61-0.83). None are present at term. Expression was largely localized to syncytiotrophoblast of both hESCBAP cells and placental material from early pregnancy. WFDC2, VTCN1 and ACTC1 have not previously been described in placenta. These results support the hypothesis that hESCBAP represent human trophoblast analogous to that of early first trimester and are a tool for discovery of factors important to this stage of placentation.
Collapse
Affiliation(s)
- Rowan M Karvas
- Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Samuel McInturf
- Division of Plant Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Jie Zhou
- Department of Obstetrics, Gynecology, and Women's Health, University of Missouri, Columbia, MO 65212, USA
| | - Toshihiko Ezashi
- Division of Animal Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Danny J Schust
- Department of Obstetrics, Gynecology, and Women's Health, University of Missouri, Columbia, MO 65212, USA
| | - R Michael Roberts
- Division of Animal Sciences, University of Missouri, Columbia, MO 65211, USA.,Department of Biochemistry University of Missouri, Columbia, MO 65211, USA
| | - Laura C Schulz
- Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA.,Department of Obstetrics, Gynecology, and Women's Health, University of Missouri, Columbia, MO 65212, USA
| |
Collapse
|
3
|
Dugina VB, Shagieva GS, Kopnin PB. Biological Role of Actin Isoforms in Mammalian Cells. BIOCHEMISTRY (MOSCOW) 2019; 84:583-592. [DOI: 10.1134/s0006297919060014] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
|
4
|
Kant S, Freytag B, Herzog A, Reich A, Merkel R, Hoffmann B, Krusche CA, Leube RE. Desmoglein 2 mutation provokes skeletal muscle actin expression and accumulation at intercalated discs in murine hearts. J Cell Sci 2019; 132:jcs.199612. [PMID: 30659114 DOI: 10.1242/jcs.199612] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 12/30/2018] [Indexed: 01/05/2023] Open
Abstract
Arrhythmogenic cardiomyopathy (AC) is an incurable progressive disease that is linked to mutations in genes coding for components of desmosomal adhesions that are localized to the intercalated disc region, which electromechanically couples adjacent cardiomyocytes. To date, the underlying molecular dysfunctions are not well characterized. In two murine AC models, we find an upregulation of the skeletal muscle actin gene (Acta1), which is known to be a compensatory reaction to compromised heart function. Expression of this gene is elevated prior to visible morphological alterations and clinical symptoms, and persists throughout pathogenesis with an additional major rise during the chronic disease stage. We provide evidence that the increased Acta1 transcription is initiated through nuclear activation of the serum response transcription factor (SRF) by its transcriptional co-activator megakaryoblastic leukemia 1 protein (MKL1, also known as MRTFA). Our data further suggest that perturbed desmosomal adhesion causes Acta1 overexpression during the early stages of the disease, which is amplified by transforming growth factor β (TGFβ) release from fibrotic lesions and surrounding cardiomyocytes during later disease stages. These observations highlight a hitherto unknown molecular AC pathomechanism.
Collapse
Affiliation(s)
- Sebastian Kant
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany
| | - Benjamin Freytag
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany
| | - Antonia Herzog
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany
| | - Anna Reich
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany
| | - Rudolf Merkel
- Forschungszentrum Jülich, Institute of Complex Systems, ICS-7, Biomechanics, 52428 Jülich, Germany
| | - Bernd Hoffmann
- Forschungszentrum Jülich, Institute of Complex Systems, ICS-7, Biomechanics, 52428 Jülich, Germany
| | - Claudia A Krusche
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany
| | - Rudolf E Leube
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany
| |
Collapse
|
5
|
Westhoff CC, Schoner K, Hartmann S, Sesterhenn AM, Moll R. Actin isoform expression patterns in adult extracardiac and cardiac rhabdomyomas indicate a different cell of origin. Virchows Arch 2017; 470:285-290. [PMID: 28091730 DOI: 10.1007/s00428-017-2069-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Revised: 01/03/2017] [Accepted: 01/06/2017] [Indexed: 11/29/2022]
Abstract
Rhabdomyomas are rare striated muscle-type tumors arising in the heart or in soft tissues. Using a monoclonal antibody specific for the cardiac isoform of α-actin (α-cardiac actin, α-CAA), differential expression patterns in striated muscle tissues were reported previously. The purpose of the present study was to determine whether the α-actin isoform specificity is maintained in rhabdomyomas according to their origin, comparing extracardiac to cardiac rhabdomyomas. We immunohistochemically investigated adult extracardiac (pharyngeal) rhabdomyomas (n = 4) and cardiac rhabdomyomas (n = 7) employing isoform-specific monoclonal antibodies. The extracardiac rhabdomyomas revealed only a few scattered α-CAA-positive tumor cells (antibody cAc1-20.42) while the cardiac rhabdomyomas exhibited abundant expression of α-CAA, indicating a close relatedness to cardiac muscle fibers. The α-skeletal actin (α-SKA) specific monoclonal antibody (3B3) produced the reverse results. General sarcomeric antibodies (HHF35 and Alpha Sr-1) displayed strong positivity in all rhabdomyomas studied. Alpha-smooth muscle actin (α-SMA) was negative or heterogeneously positive in extracardiac and cardiac rhabdomyomas. Our results suggest that despite similar morphology, the intrinsic differential alpha-actin isoform specificity of mature skeletal vs. cardiac muscle is maintained in extracardiac and cardiac rhabdomyomas. Thus, adult extracardiac rhabdomyomas differentiate towards mature skeletal muscle although they may exhibit centrally placed nuclei like cardiac muscle cells, while cardiac rhabdomyomas reflect true cardiac muscle differentiation. Our findings appear to indicate a different biological nature of cardiac and extracardiac rhabdomyomas, probably related to a different cell of origin. To our knowledge, this is the first report suggesting a derivation of extracardiac and cardiac rhabdomyomas from skeletal and cardiac muscle cells, respectively.
Collapse
Affiliation(s)
- Christina C Westhoff
- Institute of Pathology, Philipps University and University Hospital Giessen and Marburg, Baldingerstrasse, D-35043, Marburg, Germany.
| | - Katharina Schoner
- Institute of Pathology, Fetal Pathology, Philipps University and University Hospital Giessen and Marburg, Marburg, Germany
| | - Sylvia Hartmann
- Dr. Senckenberg Institute of Pathology, Goethe University, Frankfurt am Main, Germany
| | - Andreas M Sesterhenn
- Department of Otorhinolaryngology, Head and Neck Surgery, Philipps University and University Hospital Giessen and Marburg, Marburg, Germany.,Department of Otorhinolaryngology, Head and Neck Surgery, Städtisches Klinikum Solingen gGmbH, Gotenstraße 1, D-42653, Solingen, Germany
| | - Roland Moll
- Institute of Pathology, Philipps University and University Hospital Giessen and Marburg, Baldingerstrasse, D-35043, Marburg, Germany
| |
Collapse
|
6
|
Chaponnier C, Gabbiani G. Monoclonal antibodies against muscle actin isoforms: epitope identification and analysis of isoform expression by immunoblot and immunostaining in normal and regenerating skeletal muscle. F1000Res 2016; 5:416. [PMID: 27335638 PMCID: PMC4893938 DOI: 10.12688/f1000research.8154.2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 05/25/2016] [Indexed: 11/20/2022] Open
Abstract
Higher vertebrates (mammals and birds) express six different highly conserved actin isoforms that can be classified in three subgroups: 1) sarcomeric actins, α-skeletal (α-SKA) and α-cardiac (α-CAA), 2) smooth muscle actins (SMAs), α-SMA and γ-SMA, and 3) cytoplasmic actins (CYAs), β-CYA and γ-CYA. The variations among isoactins, in each subgroup, are due to 3-4 amino acid differences located in their acetylated N-decapeptide sequence. The first monoclonal antibody (mAb) against an actin isoform (α-SMA) was produced and characterized in our laboratory in 1986 (Skalli et al., 1986) . We have further obtained mAbs against the 5 other isoforms. In this report, we focus on the mAbs anti-α-SKA and anti-α-CAA obtained after immunization of mice with the respective acetylated N-terminal decapeptides using the Repetitive Immunizations at Multiple Sites Strategy (RIMMS). In addition to the identification of their epitope by immunoblotting, we describe the expression of the 2 sarcomeric actins in mature skeletal muscle and during muscle repair after micro-lesions. In particular, we analyze the expression of α-CAA, α-SKA and α-SMA by co-immunostaining in a time course frame during the muscle repair process. Our results indicate that a restricted myocyte population expresses α-CAA and suggest a high capacity of self-regeneration in muscle cells. These antibodies may represent a helpful tool for the follow-up of muscle regeneration and pathological changes.
Collapse
Affiliation(s)
- Christine Chaponnier
- Department of Pathology-Immunology, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Giulio Gabbiani
- Department of Pathology-Immunology, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| |
Collapse
|
7
|
Bird NC, Windner SE, Devoto SH. Immunocytochemistry to study myogenesis in zebrafish. Methods Mol Biol 2012; 798:153-69. [PMID: 22130836 DOI: 10.1007/978-1-61779-343-1_9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
During myogenesis, cells gradually transition from mesodermal precursors to myoblasts, myocytes, and then to muscle fibers. The molecular characterization of this process requires the ability to identify each of these cell types and the factors that regulate the transitions between them. The most versatile technique for assaying cell identities in situ is immunocytochemistry, because multiple independent molecular markers of differentiation can be assayed simultaneously. The zebrafish has developed into a popular model for the study of myogenesis, and immunocytochemical techniques have been critical. We have adapted existing protocols to optimize immunocytochemistry in zebrafish, and have tested many antibodies developed against mouse, chick, and frog muscle antigens for their cross-reactivity in zebrafish. Here, we present protocols for whole mount immunocytochemistry on both formaldehyde and Carnoy's fixed embryos as well as on sectioned zebrafish tissue. We include a table of antibodies useful for experiments on the molecular biology of myogenesis in zebrafish.
Collapse
Affiliation(s)
- Nathan C Bird
- Department of Biology, Wesleyan University, Hall-Atwater Laboratories, Middletown, CT, USA
| | | | | |
Collapse
|
8
|
Abstract
Although actin is often thought of as a single protein, in mammals it actually consists of six different isoforms encoded by separate genes. Each isoform is remarkably similar to every other isoform, with only slight variations in amino acid sequence. Nevertheless, recent work indicates that actin isoforms carry out unique cellular functions. Here, we review evidence drawn from localization studies, mouse models, and biochemical characterization to suggest a model for how in vivo mixing of actin isoforms may influence cytoskeletal function in cells. © 2010 Wiley-Liss, Inc.
Collapse
Affiliation(s)
- Benjamin J Perrin
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | | |
Collapse
|
9
|
|
10
|
Clément S, Stouffs M, Bettiol E, Kampf S, Krause KH, Chaponnier C, Jaconi M. Expression and function of alpha-smooth muscle actin during embryonic-stem-cell-derived cardiomyocyte differentiation. J Cell Sci 2006; 120:229-38. [PMID: 17179203 DOI: 10.1242/jcs.03340] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Three alpha-muscle actin isoforms are sequentially expressed during in vivo cardiac development. alpha-Smooth muscle actin is first and transiently expressed, followed by alpha-skeletal and finally alpha-cardiac actin. The significance of these transitions in actin gene expression during myogenesis remains to be determined. To understand whether actin isoforms have specific functions during cardiac development and cardiomyocyte contractility, we have hampered alpha-smooth muscle and alpha-skeletal actin expression and organization during embryonic stem cell differentiation towards cardiomyocyte. We show that the sequence of actin isoform expression displays similar pattern in the in vitro model and in mouse heart embryogenesis. Treatment with an interfering fusion peptide containing the N-terminal sequence of alpha-smooth muscle actin during a time window preceding spontaneous beating, prevents proper cardiac sarcomyogenesis, whereas alpha-skeletal actin-fusion peptide has no effect. Knockdown of alpha-smooth muscle actin in embryonic stem cells using RNA interference also affects cardiac differentiation. The application of both fusion peptides on beating embryoid bodies impairs frequency. These results suggest specific functional activities for actin isoforms in cardiogenesis and cardiomyocyte contractility.
Collapse
Affiliation(s)
- Sophie Clément
- Department of Geriatrics, Laboratory of Ageing, Geneva Hospital, Chêne-Bourg, Geneva, Switzerland.
| | | | | | | | | | | | | |
Collapse
|
11
|
Moll R, Holzhausen HJ, Mennel HD, Kuhn C, Baumann R, Taege C, Franke WW. The cardiac isoform of α-actin in regenerating and atrophic skeletal muscle, myopathies and rhabdomyomatous tumors: an immunohistochemical study using monoclonal antibodies. Virchows Arch 2006; 449:175-91. [PMID: 16715231 DOI: 10.1007/s00428-006-0220-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2005] [Accepted: 04/08/2006] [Indexed: 11/29/2022]
Abstract
The two sarcomeric isoforms of actins, cardiac and skeletal muscle alpha-actin, are highly homologous so that their immunohistochemical distinction is extremely difficult. Taking advantage of monoclonal antibodies distinguishing the two conservative amino acid exchanges near the aminoterminus, we have performed an extended immunohistochemical analysis of the cardiac alpha-actin (CAA) isoform in normal, regenerating, diseased and neoplastic human muscle tissues. Intense and uniform CAA staining is seen in fetal and adult myocardium and in fetal skeletal muscle while adult skeletal muscle is essentially negative, except for muscle spindle myocytes and a few scattered muscle fibres with overall reduced diameter. By contrast, CAA synthesis is markedly induced in regenerating skeletal muscle cells, in Duchenne muscular dystrophy and upon degenerative atrophy. CAA has also been detected in certain vascular and visceral smooth muscle cells. Among tumors, CAA has consistently been seen in rhabdomyosarcomas and rhabdomyomatous cells of nephroblastomas, whereas, smooth muscle tumors have shown only occasional staining. While the synthesis of this actin isoform is less restricted than previously thought, monoclonal antibodies against CAA provide a well-defined, reliable and sensitive diagnostic tool for the definition and detection of aberrant differentiation in diseased skeletal muscle and of striated muscle differentiation in rhabdomyosarcomas.
Collapse
Affiliation(s)
- Roland Moll
- Institute of Pathology, Philipp University of Marburg, Baldingerstrasse, D-35033 Marburg, Germany.
| | | | | | | | | | | | | |
Collapse
|
12
|
Franke WW, Borrmann CM, Grund C, Pieperhoff S. The area composita of adhering junctions connecting heart muscle cells of vertebrates. I. Molecular definition in intercalated disks of cardiomyocytes by immunoelectron microscopy of desmosomal proteins. Eur J Cell Biol 2006; 85:69-82. [PMID: 16406610 DOI: 10.1016/j.ejcb.2005.11.003] [Citation(s) in RCA: 184] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Revised: 11/18/2005] [Accepted: 11/21/2005] [Indexed: 12/17/2022] Open
Abstract
Among sarcomeric muscles the cardiac muscle cells are unique by, inter alia, a systemic and extended cell-cell contact structure, the intercalated disk (ID), comprising frequent and closely spaced arrays of plaque-coated cell-cell adhering junctions (AJs). As some of these junctions may look somewhat like desmosomes and others like fasciae adhaerentes, the dogma has emerged in the literature that IDs contain - like epithelial cells - both kinds of AJs formed by - for the most - mutually exclusive molecular ensembles. This, however, is not the case. In comprehensive immunoelectron microscopic studies of mammalian (human, bovine, rat, mouse) and non-mammalian (chicken, amphibia, fishes) heart muscle tissues, we have localized major constituents of the desmosomal plaques of polar epithelia, desmoplakin, plakophilin-2 and plakoglobin, as well as the desmosomal cadherins, desmoglein Dsg2 and desmocollin Dsc2, in both kinds of ID AJs, independent of the specific morphological appearance. The desmosomal molecules are not restricted to the desmosome-like-looking junctions but can also be detected in junctions appearing similar to the zonula or fascia adhaerens structures. These AJs of cardiac ID are therefore subsumed under the collective term area composita. We discuss our results with respect to the importance of ID junction molecules for the formation, maintenance and function of the heart, particularly in relation to recent findings that deletions of - or mutations in - genes encoding such proteins can cause severe, sometimes lethal damages.
Collapse
Affiliation(s)
- Werner W Franke
- Division of Cell Biology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
| | | | | | | |
Collapse
|
13
|
Chaudhary KW, Barrezueta NX, Bauchmann MB, Milici AJ, Beckius G, Stedman DB, Hambor JE, Blake WL, McNeish JD, Bahinski A, Cezar GG. Embryonic stem cells in predictive cardiotoxicity: laser capture microscopy enables assay development. Toxicol Sci 2005; 90:149-58. [PMID: 16357009 DOI: 10.1093/toxsci/kfj078] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Embryonic stem (ES) cells offer unprecedented opportunities for in vitro drug discovery and safety assessment of compounds. Cardiomyocytes derived from ES cells enable development of predictive cardiotoxicity models to increase the safety of novel drugs. Heterogeneity of differentiated ES cells limits the development of reliable in vitro models for compound screening. We report an innovative and robust approach to isolate ES-derived cardiomyocytes using laser microdissection and pressure catapulting (LMPC). LMPC cells were readily applied onto 96-well format in vitro pharmacology assays. The expression of developmental and functional cardiac markers, Nkx 2.5, MLC2V, GATA-4, Connexin 43, Connexin 45, Serca-2a, cardiac alpha actin, and phospholamban, among others, was confirmed in LMPC ES-derived cardiomyocytes. Functional assays exhibited cardiac-like response to increased extracellular calcium (5.4 mM extracellular Ca2+) and L-type calcium channel antagonist (1 microM nifedipine). In conclusion, laser microdissection and pressure catapulting is a robust technology to isolate homogeneous ES-derived cell types from heterogeneous populations applicable to assay development.
Collapse
Affiliation(s)
- Khuram W Chaudhary
- Pfizer Global Research and Development, Chesterfield, Missouri 63017, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Ilkovski B, Clement S, Sewry C, North KN, Cooper ST. Defining α-skeletal and α-cardiac actin expression in human heart and skeletal muscle explains the absence of cardiac involvement in ACTA1 nemaline myopathy. Neuromuscul Disord 2005; 15:829-35. [PMID: 16288873 DOI: 10.1016/j.nmd.2005.08.004] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2005] [Revised: 07/26/2005] [Accepted: 08/05/2005] [Indexed: 11/16/2022]
Abstract
Mutations in alpha-skeletal actin (ACTA1) underlie several congenital muscle disorders including nemaline myopathy (NM). Almost all ACTA1-NM patients have normal cardiac function, and, even lethally affected congenital NM patients exhibit an unremarkable gestation with decreased foetal movement just prior to birth. Although alpha-skeletal actin is thought to be the predominant sarcomeric actin in human heart (Boheler KR, Carrier L, de la Bastie D, et al. Skeletal actin mRNA increases in the human heart during ontogenic development and is the major isoform of control and failing adult hearts. J Clin Invest 1991;88:323-30 ), ACTA1-NM patients almost never exhibit a cardiac phenotype. In this study, we define the relative expression of skeletal and cardiac actin proteins in human heart and skeletal muscle. We show that alpha-cardiac actin is the predominant sarcomeric isoform in human donor hearts and in early foetal skeletal muscle development. Skeletal actin is the predominant isoform from 25 to 27 weeks gestation and is the exclusive isoform expressed in muscle from infancy through to adulthood. These findings are consistent with clinical observations of NM patients and assist us to better understand the pathogenesis of inherited myopathies and cardiomyopathies with mutations in actin.
Collapse
Affiliation(s)
- Biljana Ilkovski
- Institute for Neuromuscular Research, Children's Hospital at Westmead, Sydney, Australia
| | | | | | | | | |
Collapse
|
15
|
Agrawal PB, Strickland CD, Midgett C, Morales A, Newburger DE, Poulos MA, Tomczak KK, Ryan MM, Iannaccone ST, Crawford TO, Laing NG, Beggs AH. Heterogeneity of nemaline myopathy cases with skeletal muscle alpha-actin gene mutations. Ann Neurol 2004; 56:86-96. [PMID: 15236405 DOI: 10.1002/ana.20157] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Nemaline myopathy (NM) is the most common of several congenital myopathies that present with skeletal muscle weakness and hypotonia. It is clinically heterogeneous and the diagnosis is confirmed by identification of nemaline bodies in affected muscles. The skeletal muscle alpha-actin gene (ACTA1) is one of five genes for thin filament proteins identified so far as responsible for different forms of NM. We have screened the ACTA1 gene in a cohort of 109 unrelated patients with NM. Here, we describe clinical and pathological features associated with 29 ACTA1 mutations found in 38 individuals from 28 families. Although ACTA1 mutations cause a remarkably heterogeneous range of phenotypes, they were preferentially associated with severe clinical presentations (p < 0.0001). Most pathogenic ACTA1 mutations were missense changes with two instances of single base pair deletions. Most patients with ACTA1 mutations had no prior family history of neuromuscular disease (24/28). One severe case, caused by compound heterozygous recessive ACTA1 mutations, demonstrated increased alpha-cardiac actin expression, suggesting that cardiac actin might partially compensate for ACTA1 abnormalities in the fetal/neonatal period. This cohort also includes the first instance of an ACTA1 mutation manifesting with adult-onset disease and two pedigrees exhibiting potential incomplete penetrance. Overall, ACTA1 mutations are a common cause of NM, accounting for more than half of severe cases and 26% of all NM cases in this series.
Collapse
Affiliation(s)
- Pankaj B Agrawal
- Genomics Program and Division of Genetics, Children's Hospital Boston, MA 02115, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Ehler E, Fowler VM, Perriard JC. Myofibrillogenesis in the developing chicken heart: Role of actin isoforms and of the pointed end actin capping protein tropomodulin during thin filament assembly. Dev Dyn 2004; 229:745-55. [PMID: 15042698 DOI: 10.1002/dvdy.10482] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Recently, important differences between myofibrillogenesis in cultured cardiomyocytes vs. the three-dimensional setting in situ could be determined. We investigated thin filament assembly in situ by confocal microscopy of whole-mount preparations of immunostained embryonic chicken hearts. Of interest, a distinct localisation of different actin isoforms was observed in immature thin filaments. Cardiac alpha-actin is restricted to filaments with a length comparable to mature thin filaments as soon as the first contractions occur, while vascular alpha-actin makes up filaments that extend toward the M-band. The pointed-end actin filament capping protein tropomodulin can be found initially in close association with the plasma membrane, but attains its mature localisation pattern at the ends of the thin filaments only comparatively late during myofibrillogenesis. Thus tropomodulin acts as a length stabilising element of actin filaments also in developing cardiomyocytes in situ, but plays an additional role together with membrane-associated actin filaments in the earliest steps of myofibril assembly.
Collapse
Affiliation(s)
- Elisabeth Ehler
- Institute of Cell Biology, ETH-Zürich Hönggerberg, Zürich, Switzerland
| | | | | |
Collapse
|
17
|
Peitsch WK, Hofmann I, Endlich N, Prätzel S, Kuhn C, Spring H, Gröne HJ, Kriz W, Franke WW. Cell biological and biochemical characterization of drebrin complexes in mesangial cells and podocytes of renal glomeruli. J Am Soc Nephrol 2003; 14:1452-63. [PMID: 12761245 DOI: 10.1097/01.asn.0000069222.63700.de] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Drebrins are actin-binding proteins (ABP) initially identified in and thought to be specific for neuronal cells, where they appear to contribute to the formation of cell processes. Recent studies have also detected the isoform drebrin E2 in a wide range of non-neuronal cell types, notably in and near actin-rich lamellipodia and filopodia. The present study demonstrates drebrin enrichment in renal glomeruli. Immunohistochemistry and double-label confocal laser scanning microscopy have shown intense drebrin reactions in the mesangial cells of diverse mammalian species. In adult human and bovine kidneys, drebrin is, in addition, markedly enriched in the foot processes of podocytes, as also demonstrable by immunoelectron microscopy. By contrast, the podocytes of rodent glomeruli appear to contain significant drebrin concentrations only during early developmental stages. In differentiated murine podocytes cultured in vitro, however, drebrin is concentrated in the cell processes, where it partially codistributes with actin and other ABP. In biochemical analyses using protein extracts from renal cortices, large (approximately 20S) complexes ("drebrosomes") were found containing drebrin and actin. These findings confirm and extend our hypothesis that drebrin is involved in the regulation of actin dynamics also outside the nervous system. Clearly, drebrin has to be added to the ensemble of ABP regulating the actomyosin system and the dynamics of mesangial cells and foot processes in podocytes.
Collapse
Affiliation(s)
- Wiebke K Peitsch
- Division of Cell Biology, German Cancer Research Center, Heidelberg, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Möbus VJ, Gerharz CD, Weikel W, Merk O, Dreher L, Kreienberg R, Moll R. Characterization of a human carcinosarcoma cell line of the ovary established after in vivo change of histologic differentiation. Gynecol Oncol 2001; 83:523-32. [PMID: 11733966 DOI: 10.1006/gyno.2001.6425] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVES Cell lines are valuable in vitro models for clinical and basic research. Most ovarian cancer cell lines described are serous cystadenocarcinomas or poorly differentiated adenocarcinomas. The establishment of ovarian cancer cell lines with rare histologic differentiation is especially of interest. We describe the establishment of a carcinosarcoma cell line of the ovary after in vivo selection. METHODS The cell line OV-MZ-22 was established from a solid tumor mass in the upper abdomen. At the time of establishment, the patient underwent secondary debulking and was pretreated with six cycles of cis-platinum/epirubicin/cyclophosphamide. Features of the cell line studied included morphology, ultrastructure, heterotransplantation, chromosome analysis, and analysis of intermediate filament proteins and actins by immunocytochemistry. RESULTS The first histologic report of the patient described a papillary cystadenocarcinoma, which changed to a carcinosarcoma with predominantly sarcomatous differentiation at secondary debulking. This cell line is aneuploid and shows no expression of the tumor-associated antigens CA-125 and CEA, but an overexpression of MDR-1, lung resistance protein, p53, and topoisomerase I and II, but not of multidrug-resistance-associated protein. The cell line did not give rise to transplant tumors in nude mice. The histologic and immunocytochemical comparison of the primary and the relapsed tumor proved evidence of an in vivo change of differentiation from predominantly papillary cystadenocarcinoma to carcinosarcoma. Morphological characteristics and intermediate filament pattern underlined the sarcomatous differentiation and origin of this cell line. The differentiation phenotype of OV-MZ-22 cells is that of smooth-muscle cells. CONCLUSION The change of histologic differentiation was apparently due to a selection process caused by platinum-containing chemotherapy. The origin of the cell line and its rarity make this new line an appropriate tool for further investigation.
Collapse
Affiliation(s)
- V J Möbus
- Department of Obstetrics and Gynecology, Städtische Kliniken Frankfurt a.M., Frankfurt, Germany.
| | | | | | | | | | | | | |
Collapse
|
19
|
Abstract
Actin, one of the main proteins of muscle and cytoskeleton, exists as a variety of highly conserved isoforms whose distribution in vertebrates is tissue-specific. Synthesis of specific actin isoforms is accompanied by their subcellular compartmentalization, with both processes being regulated by factors of cell proliferation and differentiation. Actin isoforms cannot substitute for each other, and the high-level synthesis of exogenous actins leads to alterations in cell organization and morphology. This indicates that the highly conserved actins are functionally specialized for the tissues in which they predominate. The first goal of this review is to analyze the data on the polymerizability of actin isoforms to show that cytoskeleton isoactins form less stable polymers than skeletal muscle actin. This difference correlates with the dynamics of actin microfilaments versus the stability of myofibrillar systems. The three-dimensional actin structure as well as progress in the analysis of conformational changes in both the actin monomer and the filament allows us to view the data on the structure and polymerization of isoactins in terms of structure-function relationships within the actin molecule. Most of the amino acid substitutions that distinguish actin isoforms are located apart from actin-actin contact sites in the polymer. We suggest that these substitutions can modulate the ability of actin monomers to form more or less stable polymers by long-range (allosteric) regulation of the contact sites.
Collapse
Affiliation(s)
- S Y Khaitlina
- Institute of Cytology, Russian Academy of Sciences, St. Petersburg
| |
Collapse
|
20
|
Rudy DE, Yatskievych TA, Antin PB, Gregorio CC. Assembly of thick, thin, and titin filaments in chick precardiac explants. Dev Dyn 2001; 221:61-71. [PMID: 11357194 DOI: 10.1002/dvdy.1125] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
De novo cardiac myofibril assembly has been difficult to study due to the lack of available cell culture models that clearly and accurately reflect heart muscle development in vivo. However, within precardiac chick embryo explants, premyocardial cells differentiate and commence beating in a temporal pattern that corresponds closely with myocyte differentiation in the embryo. Immunofluorescence staining of explants followed by confocal microscopy revealed that distinct stages of cardiac myofibril assembly, ranging from the earliest detection of sarcomeric proteins to the late appearance of mature myofibrils, were consistently recognized in precardiac cultures. Assembly events involved in the early formation of sarcomeres were clearly visualized and accurately reflected observations described by others during chick heart muscle development. Specifically, the early colocalization of alpha-actinin and titin dots was observed near the cell periphery representing I-Z-I-like complex formation. Myosin-containing thick filaments assembled independently of actin-containing thin filaments and appeared centered within sarcomeres when titin was also linearly aligned at or near cell borders. An N-terminal epitope of titin was detected earlier than a C-terminal epitope; however, both epitopes were observed to alternate near the cell periphery concomitant with the earliest formation of myofibrils. Although vascular actin was detected within cells during early assembly stages, cardiac actin predominated as the major actin isoform in mature thin filaments. Well-aligned thin filaments were also observed in the absence of organized staining for tropomodulin at thin filament pointed ends, suggesting that tropomodulin is not required to define thin filament lengths. Based on these findings, we conclude that the use of the avian precardiac explant system accurately allows for direct investigation of the mechanisms regulating de novo cardiac myofibrillogenesis.
Collapse
Affiliation(s)
- D E Rudy
- Department of Cell Biology and Anatomy, University of Arizona, Tucson, Arizona, USA
| | | | | | | |
Collapse
|
21
|
Ojima K, Lin Z, Bang ML, Holtzer S, Matsuda R, Labeit S, Sweeney H, Holtzer H. Distinct families of Z-line targeting modules in the COOH-terminal region of nebulin. J Cell Biol 2000; 150:553-66. [PMID: 10931867 PMCID: PMC2175182 DOI: 10.1083/jcb.150.3.553] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
To learn how nebulin functions in the assembly and maintenance of I-Z-I bands, MYC- and GFP- tagged nebulin fragments were expressed in primary cultured skeletal myotubes. Their sites of incorporation were visualized by double staining with anti-MYC, antibodies to myofibrillar proteins, and FITC- or rhodamine phalloidin. Contrary to expectations based on in vitro binding studies, none of the nebulin fragments expressed in maturing myotubes were incorporated selectively into I-band approximately 1.0-micrometer F-alpha-actin-containing thin filaments. Four of the MYC/COOH-terminal nebulin fragments were incorporated exclusively into periodic approximately 0.1-micrometer Z-bands. Whereas both anti-MYC and Rho-phalloidin stained intra-Z-band F-alpha-actin oligomers, only the latter stained the pointed ends of the polarized approximately 1.0-micrometer thin filaments. Z-band incorporation was independent of the nebulin COOH-terminal Ser or SH3 domains. In vitro cosedimentation studies also demonstrated that nebulin SH3 fragments did not bind to F-alpha-actin or alpha-actinin. The remaining six fragments were not incorporated into Z-bands, but were incorporated (a) diffusely throughout the sarcoplasm and into (b) fibrils/patches of varying lengths and widths nested among normal striated myofibrils. Over time, presumably in response to the mediation of muscle-specific homeostatic controls, many of the ectopic MYC-positive structures were resorbed. None of the tagged nebulin fragments behaved as dominant negatives; they neither blocked the assembly nor induced the disassembly of mature striated myofibrils. Moreover, they were not cytotoxic in myotubes, as they were in the fibroblasts and presumptive myoblasts in the same cultures.
Collapse
Affiliation(s)
- K. Ojima
- Department of Cell and Developmental Biology, The School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Z.X. Lin
- Department of Cell Biology, Beijing Institute for Cancer Research, Beijing Medical University, Beijing 100034, China
| | | | - S. Holtzer
- Department of Cell and Developmental Biology, The School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - R. Matsuda
- Department of Life Science, University of Tokyo, Tokyo, Japan 153-8092
| | - S. Labeit
- Department of Anesthesiology and Intensive Operative Care, Klinikum, Mannheim, Germany
| | - H.L. Sweeney
- Department of Physiology, The School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - H. Holtzer
- Department of Cell and Developmental Biology, The School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| |
Collapse
|
22
|
Abstract
Using immunohistochemistry in diagnosing neuromuscular diseases is meant to enhance the diagnostic yield in two ways. The first application aims at visualizing molecules which are developmentally, neurally, and/or immunologically regulated and not expressed by normal muscle. They are upregulated in pathological conditions and may help assign a given muscular biopsy to one of the main diagnostic entities (muscular dystrophies, inflammatory myopathy, neurogenic atrophy). In the past, muscle-specific molecules with a defined expression pattern during fetal myogenesis served as antigens, with the rationale that the developmental program was switched on in new fibers. Recently, myofibers in diseased muscle are thought of as targets of stimuli which are released by macrophages in muscular dystrophy, by lymphocytes in inflammatory myopathies, or by a lesioned peripheral nerve in neurogenic atrophies. This has somewhat blurred the borders between the diagnostic groups, for certain molecules, e.g. cytokines, may be upregulated after experimental necrotization, denervation, and also in inflammatory myopathies. In the second part of this review we summarise the experiences of a Centre in the North of England that specialises in the diagnosis and clinical support of patients with muscular dystrophy. Emphasis is placed on the use of protein expression to guide mutation analysis, particularly in the limb-girdle muscular dystrophies (a group of diseases that are very difficult to differentiate on clinical grounds alone). We confirm that genetic analysis is essential to corroborate the results of protein analysis in certain conditions (particularly in calpainopathy). However, we conclude that analysing biopsies for abnormal protein expression is very useful in aiding the decision between alternative diagnoses.
Collapse
Affiliation(s)
- A Bornemann
- Institute of Brain Research, University of Tübingen, Germany.
| | | |
Collapse
|
23
|
Clément S, Chaponnier C, Gabbiani G. A subpopulation of cardiomyocytes expressing alpha-skeletal actin is identified by a specific polyclonal antibody. Circ Res 1999; 85:e51-8. [PMID: 10559147 DOI: 10.1161/01.res.85.10.e51] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The NH(2)-terminal decapeptide of alpha-skeletal actin that contains a primary sequence specific for this isoform was used to raise a polyclonal antibody in rabbits. Using sequential affinity chromatography, we recovered from serum antibodies reacting exclusively with alpha-skeletal actin when tested by immunoblotting and immunofluorescence. Epitope mapping by means of competition assays with synthetic peptides indicated that the acetyl group and the first 9 amino acids are essential for specificity. The monospecific antibody was then used to investigate the distribution of alpha-skeletal actin in the myocardium of newborn and normal or hypertensive (with or without fibrotic areas) adult rats. Immunostaining of normal heart revealed that alpha-skeletal actin is diffusely distributed within practically all myocardial fibers of the newborn rat, whereas it is restricted to a small proportion of adult rat cardiomyocytes, which appear intensely stained. A correlation, albeit not complete, was found between the distribution of alpha-skeletal actin and beta-myosin heavy chain. During cardiac hypertrophy induced by aortic ligature between the renal arteries, the expressions of alpha-skeletal actin mRNA and protein were increased. The distribution of immunostaining had a focal pattern similar to that of normal adult rats, reactive fibers being more numerous and more intensely stained compared with normal myocardium. Positive fibers were particularly abundant at the periphery of fibrotic areas. Using this antibody, we have demonstrated for the first time the differential distribution of alpha-skeletal actin in heart tissues. Changes in the distribution of this isoform in hypertrophic heart provide new insight into the mechanisms by which the heart adapts to work overload. This antibody will prove useful in exploring the mechanisms of expression of alpha-skeletal actin and in defining its role in physiological and pathological situations.
Collapse
Affiliation(s)
- S Clément
- Department of Pathology, University of Geneva-CMU, Geneva, Switzerland
| | | | | |
Collapse
|
24
|
Munz B, Wiedmann M, Lochmüller H, Werner S. Cloning of novel injury-regulated genes. Implications for an important role of the muscle-specific protein skNAC in muscle repair. J Biol Chem 1999; 274:13305-10. [PMID: 10224091 DOI: 10.1074/jbc.274.19.13305] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To gain insight into the molecular mechanisms underlying the wound repair process, we searched for genes that are regulated by skin injury. Using the differential display reverse transcription-polymerase chain reaction technique, we identified a gene that was strongly induced as early as 12 h after wounding. Sequence analysis revealed the identity of the corresponding protein with skeletal muscle nascent polypeptide-associated complex (skNAC), a recently identified muscle-specific transcription factor. By in situ hybridization and immunohistochemistry, we demonstrated the specific expression of skNAC in skeletal muscle cells of the panniculus carnosus at the wound edge. Furthermore, in vitro studies with cultured myoblasts revealed expression of skNAC in differentiating and differentiated, but not in proliferating, nondifferentiated cells. Differentiation of cultured myoblasts was accompanied by simultaneous expression of skNAC and the muscle-specific transcription factor myogenin. Our results provide the first evidence for a role of skNAC in muscle repair processes. Furthermore, they demonstrate the usefulness of our approach in identifying new players in wound repair.
Collapse
Affiliation(s)
- B Munz
- Max-Planck-Institut für Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany
| | | | | | | |
Collapse
|
25
|
Lin Z, Hijikata T, Zhang Z, Choi J, Holtzer S, Sweeney HL, Holtzer H. Dispensability of the actin-binding site and spectrin repeats for targeting sarcomeric alpha-actinin into maturing Z bands in vivo: implications for in vitro binding studies. Dev Biol 1998; 199:291-308. [PMID: 9698448 DOI: 10.1006/dbio.1998.8920] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
To explore the roles of specific domains of sarcomeric alpha-actinin (s-alpha-actinin) in the assembly and maintenance of striated myofibrils, myogenic cultures were transfected with four MYC-tagged s-alpha-actinin peptides. They were: (1) full-length sarcomeric alpha-actinin, (2) an N-terminal deletion that removed the actin-binding site only (MYC/A-), (3) a peptide that consisted of the actin-binding site only (MYC/A+), and (4) an N-terminal deletion that removed the EF-hands and titin-binding domains (MYC/EFT-). While cytotoxic in replicating myogenic cells, as they were in PtK2 cells, the four MYC peptides were not cytotoxic in postmitotic myotubes. In myotubes each of the four different MYC peptides were promptly and selectively incorporated into normal Z bands. The incorporation of MYC/A-, MYC/A+, and MYC/EFT- into Z bands suggests that (a) the actin-binding site, (b) the spectrin-repeats believed to be responsible for anti-parallel dimerization, and (c) the C-terminal EF-hands and titin-binding domains are each dispensable for targeting s-alpha-actinin/MYC peptides into Z bands. These findings could not have been predicted from the behavior of alpha-actinin (a) in binding assays in cell-free systems or (b) when expressed in transfected nonmuscle cells.
Collapse
Affiliation(s)
- Z Lin
- Department of Cell Biology, Beijing Institute for Cancer Research, Beijing Medical University, China
| | | | | | | | | | | | | |
Collapse
|